Display technology pervades all aspects of present day life, from televisions to automobile dashboards to lap top computers to wrist watches. At the present time, cathode-ray tubes (CRTs) dominate display applications in the 10-40 inch (diagonal) display size. CRTs, however, have many disadvantages including height, lack of ruggedness, cost, and the need for very high driving voltages.
Recently, passive-matrix liquid-crystal displays (LCDs) and active-matrix liquid crystal displays (AMLCDs) have become dominant in midrange display applications because of their use in lap top computers. For smaller pixel sizes and also for large projection displays, the AMLCD is becoming increasingly important. A major drawback of AMLCDs, however, is the requirement of a back light that substantially increases the size and weight of the display. It also leads to reduced efficiency since the back illumination is applied continuously even for pixels in the off state.
Another approach is the deformable-mirror display (DMD) based on single-crystal silicon technology. In this approach, a micro-machined mirror structure is oriented in either a reflective or dispersive mode depending whether a logic "1" or logic "0" has been written into a corresponding cell. DMD displays must operate in the reflective mode, thus, the optics are more complicated and not as compact or efficient as transmissive or emissive displays. Additionally, like AMLCDs, DMDs require an external light source, thus, they are larger and less efficient than the self-emissive displays.
Field-emission displays (FEDs) may also be considered for many applications. However, FEDs have many of the disadvantages associated with CRTs, particularly the need for cathode voltages over 100 volts, and the corresponding requirement that the thin film transistors (TFTs) have low leakage current. FEDs have relatively lower overall luminous efficiencies due to the reduced efficiency of "lower-voltage" phosphors and the use of high voltage control voltages.
Finally, another type of display, an active matrix light emitting diode (AMEL) display, emits light by passing a current through a light emitting material. In the case of an EL, an alternating current (AC) is passed through an inorganic light emitting material (e.g., PN junction is formed from inorganic semiconductor material such as silicon or gallium arsenide. The inorganic light emitting material is arranged such that dielectrics are present on either side of the emitting material. Due to the existence of the dielectrics, relatively high voltages are required to generate sufficient light from the emitting material. The relatively high voltages are typically between 100-200 volts.
The use of an AC voltage and other factors limit the efficiency of the overall display.
Also, with respect to the stability of inorganic LED displays, the brightness of the light emitting material saturates with applied voltage after a rapid transition from off to on. If the display is operated in a "fully on" and "fully off" mode, any shift in transition voltage with time has only a minimal effect on brightness.
With these disadvantages of the various display technologies in mind, a better type of display would be desirable which requires less voltage, is more efficient and is generally more advantageous for all types of display applications.